Performance enhancement of wind turbine power regulation by switched linear control

Abstract

Power regulation of horizontal-axis grid-connected up-wind constant-speed pitch-regulated wind turbines presents a demanding control problem, with the plant, actuation system and control objectives all strongly nonlinear. In this paper, a novel switched linear approach is devised. Conventional linear control and a nonlinear controller which, in some sense, optimizes performance across the operating envelope provide benchmarks against which the switched control strategy is compared. In comparison with conventional linear control, the switched linear strategy reduces the peak power excursions experienced and the time spent at high power levels, with a consequent reduction in drive-train loads. It achieves very similar performance to the more complex nonlinear controller; that is, the performance is near optimal over the operational envelope. Moreover, in contast to nonlinear control, it admits straightforward and rigorous analysis and permits direct exploitation of the knowledge and experience accumulated with linear control. Hence, switched linear control is more suited for application to wind turbines than the nonlinear control strategy. The improvement in performance, in comparison to conventional linear control, is substantial.